Yokogawa Integral Oxygen Analyzer ZR202 - Manual (Page 182)

<12. Troubleshooting>
12-12
IM 11M12A01-02E
12.3.2 Measured Value Lower Than True Value
<Causes and Countermeasures>
(1) The measuring gas pressure becomes lower.
Where an increment of the measured value due to pressure change cannot be neglected,
take measures referring to subsection 12.3.1 (1).
(2) Moisture content in a reference gas changes (decreases) greatly.
If air at the detector installation site is used for the reference gas, large change of moisture
content in the air may cause an error in measured oxygen concentration value (vol% O
2
).
When this error is not ignored, use a gas in which moisture content is constant such as
instrument air in almost dry condition as a reference gas.
In addition, change of moisture content in exhaust gas after combustion is also considered
as a cause of error. However, normally this error is negligible.
(3) Calibration gas (zero gas) is mixed into the detector due to leakage.
If the zero gas is mixed into the detector due to leakage as a result of failure of the valve
provided in the calibration gas tubing system, the measured value shows a value a little
lower than normal.
Check valves (needle valves, check valves, solenoid valves for automatic calibration,
etc.) in the calibration gas tubing system for leakage. For manual valves, check them after
confirming that they are in a fully closed situation.
(4) Combustible components exist in the sample gas. If combustible components exist in the
sample gas, they burn in the sensor and thus oxygen concentration decreases.
Check that there are no combustible components.
(5) Temperature of the detector cell reaches 750 °C or more.
12.3.3 Measurements Sometimes Show Abnormal Values
<Cause and Countermeasures>
(1) Noise may be mixing in with the converter from the detector output wiring.
Check whether the converter and detector are securely grounded.
Check whether or not the signal wiring is laid along other power cords.
(2) The converter may be affected by noise from the power supply.
Check whether or not the converter power is supplied from the same outlet, switch, or
breaker as other power machines and equipment.
(3) Poor wiring contact
If there is poor contact in the wiring, the sensor voltage or thermocouple emf (voltage) may
vary due to vibration or other factors.
Check whether or not there are loose points in the wiring connections or loose crimping
(caulking) at the crimp-on terminal lugs.
(4) Combustible components in the sample gas may be getting into the sensor.
If the combustible components show signs of dust, the abnormality may be improved by
mounting a dust-removing filter K9471UA.
(5) There may be a crack in the sensor or leakage at the sensor-mounting portion.
If the indication of concentration varies in synchronization with the pressure change in the
furnace, check whether or not there is a crack in the sensor or whether the sensor flange is
sticking tightly to the probe-attaching face with the metal O-ring squeezed.
(6) There may be leakage in the calibration gas tubing
In the case of a negative furnace inner pressure, if the indication of concentration varies with
the pressure change in the furnace, check whether or not there is leakage in the calibration
gas tubing.
8th Edition : Jan.13,2012-00